[Groxx]

I don't know of any way to control the setting automatically (sometimes there are special-permission non-standard/undocumented intents for settings though), but as a maybe-close-enough you can turn on grayscale color correction (in accessibility -> color & motion, in my phone) and add a quick-settings tile to toggle it.

[froindt]

I'm on a Pixel 10 for these instructions, not sure if other manufacturers offer the same options.

Modes is an available option in the tile list. You can go to Modes, create a custom mode, and under display options you can set greyscale. You can also set modes to turn on automatically based on calendar events or a schedule. Notification tweaks are also available in the same area.

[striking]

You can also use one of the accessibility shortcuts to trigger it quickly (both volume buttons held, triple tap, two fingers from bottom) if so configured